Morphological variation in forelimb bones has been tied to substrate use in Cercopithecidae. Studies of the distal humerus and proximal ulna (Rector et al., 2018) suggest that African and Asian monkeys’ locomotor repertoires can be distinguished through analysis of variation of the elbow joint. Given that the scapula may be directly involved in weight-bearing during locomotion - similar to the elbow - the relationship between morphological variation and arboreality in the glenoid cavity, acromion, and coracoid process may be analogous. Using a Microscribe, 25 landmarks were collected to capture the shape of the scapula from a sample of 50+ extant Cercopithecidae. Each species was placed in a locomotor category including ground quadrupedalism, branch quadrupedalism, arm-swinging, and branch quadrupedalism, and branch and ground quadrupedalism based on their primary locomotor strategy during traveling. Variation was analyzed using 3D geometric morphometric PCA, PGLs, and phylogenetic ANOVAs to determine if differential substrate use can be identified through analysis of shape variation in the scapulae of Cercopithecidae. Results suggest that scapular morphology is more variable in branch quadrupedal cercopithecids than ground quadrupedal ones. However, variation in the scapula can be used to successfully differentiate ground quadrupeds and branch quadrupeds in modern Cercopithecidae. As a valuable factor in the ecology of these primates, this locomotor behavior contributes information on niche differentiation, resource competition, and community organization in living and fossil primates.
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